Prostaglandin analogs

ABSTRACT

The compound 6,9-deepoxy-6,9-(phenylimino)-Δ 6 ,8 -prostaglandin I 1 , potassium salt and compositions thereof.

This application is a continuation of application 571,238 filed Jan. 16, 1984, now abandoned.

FIELD OF INVENTION

This invention is the novel compound 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁ potassium salt and compositions thereof.

BACKGROUND OF INVENTION

The solid-state chemical stability of a compound sometimes can be influenced by the selection of an appropriate salt form. However, there are no established general principles one can follow in improving solid-state stability through salt modification. For a review of information relating to the selection of "Pharmaceutical Salts" see S. M. Berge, et al., J. Pharm. Sci. 66, pp. 1-19 (1977).

The free acid of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁ and related analogs are known compounds having utility as antiasthmatic agents. See, e.g., U.S. Pat. No. 4,294,759 issued Oct. 13, 1981. The compound of the present invention, i.e., the potassium salt of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁, possesses a number of advantageous physical properties over the free acid rendering said potassium salt a markedly superior product candidate.

SUMMARY OF INVENTION

This invention is the potassium salt of the compound 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁, having the structure set forth on the formula sheet as Formula I. The compound and compositions of this invention are useful in the prophylactic or therapeutic treatment of allergy of a reagin or non-reagin mediated nature. Thus the compound and compositions of the present invention are useful in treating asthma, as well as allergic rhinitis, food allergy and urticaria.

DETAILED DESCRIPTION OF INVENTION

The potassium salt of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁ is useful in the same manner and is administered in the same manner and at the same dosage as is described for the pharmaceutically useful compounds described and claimed in U.S. Pat. No. 4,294,759. Also, pharmaceutical compositions of the potassium salt of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁ are useful in the same manner, and are of the same type and are prepared in the same manner as the compositions described in U.S. Pat. No. 4,294,759. The disclosure of U.S. Pat. No. 4,294,759 and in particular the portion appearing on from column 12, line 14 through column 14, line 53 is incorporated herein by reference.

The compound of this invention is also useful in preventing or inhibiting the hypersecretion of mucus in the respiratory tract of warm blooded animals as generally described in U.S. application Ser. No. 529,798, filed Sept. 6, 1983, now abandoned.

The potassium salt of the compound 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁ possesses advantageous physical properties including ease of crystallization, high melting point, high water solubility, and low solubility in fluorinated and fluorochlorinated liquified propellants as compared to the free acid of said compound. More significantly the potassium salt of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁ unexpectedly exhibits an improved solid-state stability over the free acid or the sodium salt. The following tabulations of data demonstrate the differences in the physico-chemical characteristics of the free acid, the sodium salt and the potassium salt of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁. As a result of the physical properties of the potassium salt it offers significant advantages over the corresponding free acid or sodium salt, for example, in the long term storage of bulk drug and in prolonging the shelf-life of pharmaceutically useful formulations of said salt form, such as, suspension formulations for aerosol administration.

                                      TABLE I                                      __________________________________________________________________________     Physico-Chemical Data                                                                                 Sodium Potassium                                        Property                                                                               Value Desired                                                                           Free Acid                                                                            Salt   Salt                                             __________________________________________________________________________     1 Ease of                                                                              Easily   --    Acceptable                                                                            Acceptable                                         synthesis                                                                            crystallized                                                           2 Character-                                                                           Passes profile                                                                          Pass  (.82% H.sub.2 O).sup.a                                                                Pass                                               izability                                                                            (+ low mois-          (.42% H.sub.2 O)                                         ture content                                                                   after air                                                                      equilibration)                                                         3 Water Dissolves                                                                               1 μg/ml                                                                           Soluble                                                                               Soluble                                            solubility                                                                           readily in                                                                     water                                                                  4 Trichloro-                                                                           Low      .38 μg/ml                                                                         --     0.43 μg/ml                                      trifluoro-                                                                     ethane                                                                         solubility                                                                   5 Melting                                                                              High (>100° C.)                                                                  135-140                                                                              >175   >175                                               point                                                                          (microniz-                                                                     ability)                                                                     6 Solild state                                                                         <2% degrada-                                                                            >10%  >>50%  <2%                                                stability                                                                            tion (2 months                                                           (see Table                                                                           at 33° C.)                                                        II)                                                                          7 Specific                                                                             1.3-1.6.sup.b                                                                           --    1.18   1.20                                               gravity                                                                      __________________________________________________________________________      .sup.a Initial analysis acceptable but later assays (HPLC) unacceptable        due to solidstate decomposition.                                               .sup.b Specific gravities below this range may require incorporation of        other high density solids into an aersol suspension.                     

                  TABLE II                                                         ______________________________________                                         Solid-State Stability                                                                      Percent of Theory                                                                                         Potassium                               Storage   Time    Free   Sodium                                                                               Potassium                                                                              Salt                                    Conditions                                                                               (days)  Acid   Salt  Salt    Micronized                              ______________________________________                                         Dark, 4°                                                                           0      --     101   100     --                                                19      --     87    --      --                                                46      --     77    --      --                                                66      --     --    102     --                                                189     --     --    101     --                                      Dark, 33°                                                                          0      100    101   100     100                                               19      98     61    100     --                                                40      94     --    100     --                                                66      89     --    100     --                                                100     --     --     97     97                                                189     65     --     98     --                                                216     --     --     98     98                                                289     46     --     96     --                                                405     19     --     96     --                                      High       0      100    101   100     --                                      intensity 19      55      3     48     --                                      light, 33°                                                               Dark,     0      Free flowing crystalline solids                              75% R.H..sup.a, 30°                                                               19      same   same  glass                                           (visual                                                                        observation)                                                                   Trichloro-                                                                                0      100    --    100     --                                      trifluoro-                                                                               26      94     --    100     --                                      ethane suspen-                                                                 sion, dark, 30°                                                         ______________________________________                                          .sup.a R.H. means relative humidity.                                     

As seen from the tabulated data the most striking and dramatic difference among the three compounds is their solid-state stability. The rank order of stability of the compounds when protected from light during storage, which is the recommended manner of storage, at 33° was potassium salt>free acid>sodium salt.

The solubility of the compounds in trichlorotrifluoroethane, a high molecular weight fluorochlorinated alkane liquid propellant, was determined as follows. Suspensions of each compound were prepared at concentrations of ˜1 mg/ml in trichlorotrifluoroethane in 30 ml glass vials sealed using polytetrafluoroethylene lined caps. These vials were wrapped with aluminum foil and shaken at ˜25° C. After 26 days shaking the samples were filtered. Three successive 5 ml fractions were collected from the filter and analyzed to test for adsorption. (No adsorption was observed.)

The 5 ml samples were transferred to 5 ml volumetric flasks and solvent was evaporated under nitrogen. The residue was redissolved in 1 ml methanol and diluted to 5 ml with 30% CH₃ CN. Samples were assayed by high pressure liquid chromatography.

The solid-state stability studies were performed as follows. Approximately 10-15 mg of the free acid or a salt was placed in either clear glass vials or amber vials wrapped in aluminum foil and stored under various conditions as listed below:

(a) Refrigerated at about 4° C. (dark).

(b) High Intensity Light Box at about 33° C. and relative humidity <15%. (Light Box contained 6-15 watt fluorescent bulbs 41/2 inches above the powder surface.) Sample vials were placed on their sides with powder spread evenly on the vial wall.

(c) 30° C./75% relative humidity/dark-vials were capped loosely.

(d) Suspended in trichlorotrifluoromethane and shaken continuously for 26 days.

At various times, 1-1.5 mg samples were dissolved in methanol, diluted to a prescribed volume with water, and analyzed by high pressure liquid chromatography versus reference standard of the free acid stored at -20° C. Chromatographic conditions were similar to those described previously.

To obtain specific gravity data approximate densities were obtained using a volume displacement procedure. To a 5 ml weighed pycnometer was added 200-300 mg of salt and acetonitrile added to fill. The salt suspensions were sonicated to remove entrapped air and equilibrated to 20° C. in a water bath. The salt densities were estimated by standard methods of calculation.

EXAMPLE 1 6,9-Deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁, potassium salt

A tetrahydrofuran-H₂ O solution (10 ml:10 ml) of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁ free acid was adjusted to pH 7.5 with concentrated KOH. An additional 90 ml of water was added, pH was readjusted to 8.5, and the solution was freeze dried. The freeze-dried product was recrystallized in methanol-acetonitrile, dried at 55° C./high vac overnight, and equilibrated with laboratory atmosphere. M.P. 176° dec.

EXAMPLE 2 6,9-Deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁, sodium salt

A solution of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁ free acid in 5.4 ml of 1N methanolic NaOH was filtered, washing the filter with 10 ml of methanol. Acetonitrile was slowly added to the solution while stirring resulting in crystallization of an off-white solid. After 2-3 hours stirring the solid was collected, dried overnight at 55° C., then equilibrated with laboratory atmosphere for about 4 hours. M.P. 177° C.

EXAMPLE 3

The following illustrates the aerosol suspension formulation for inhalation of the compound of this invention.

    ______________________________________                                                                Weight Percent                                          ______________________________________                                         (a) 6,9-deepoxy-6,9-(phenylimino)-Δ.sup.6,.sup.8 -prosta-                                             0.714                                                 glandin I.sub.1, potassium salt                                            (b) sorbitan trioleate       0.500                                             (c) dichlorotetrafluoroethane                                                                               98.786                                                                         100.000                                           ______________________________________                                    

Materials (a) to (c) are packaged in suitable (aluminum) containers equipped with a metering valve designed to meter 50 mcl per dose, an equivalent of 0.5 mg of compound (a).

EXAMPLE 4

To prepare a typical powder for inhalation, 2 g of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁, potassium salt and sufficient lactose to make 8 g of mixture are comminuted and placed in hard filled capsules designed for use in a device that permits inspiration of the powder by a patient. Each capsule will deliver 40 mg of powder which is equivalent to 10 mg of drug. 

I claim:
 1. A compound which is the potassium salt of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁.
 2. A pharmaceutical composition which comprises an effective antiallergic amount of the potassium salt of 6,9-deepoxy-6,9-(phenylimino)-Δ6,8-prostaglandin I₁ and a significant amount of a pharmaceutical carrier.
 3. A composition of claim 2 which is in the form of a powdered aerosol.
 4. A composition of claim 2 which is in the form of a liquid aerosol. 